High-frequency dielectric and magnetic furnace



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C. T. ALLCUTT HIGH FREQUENCY DIELECTRIC AND MAGNETIC FURNACE Filed Dec. 29. 1923 W my Q M WITNESSES:

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HIGH- FREQUENCY DIELECTRIC AND MAGNETIC FURNACE.

Application filed December 28, 1928. Serial No. 683,875.

, To all whom it may concern:-

Be it known that I, CHESTER T. ALLoU'r'r, a citizen of the United States, and a resldent of Pittsburgh, in the'county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in High- Frequency Dielectric and Magnetic Furnaces, of which the following is a specificatio a My invention relates to electric furnaces and more particularly to furnaces that are heated by means of the action of dielectric and of electromagnetic fields.

The object of my invention is to provide a system for heatingmasses of material having a relativel hlgh negative temperature co-efiic'ient o reslstivity, by means of high frequency and. high voltage electric and electromagnetic fields.

In the single sheet of drawings,

Figure 1 is a schematic diagram of connections and of a furnace embodying my invention, I Fig.2 is a top plan view of the furnace illustrated in section in Fig- 1 of the drawing, and I Fig. 3 is a schematic drawing of a furnace and system embodying my invention.

In my copending application, Serial No.

671,113; filed Oct. 27, 1923, and assigned to the Westinghouse Electric and Manufacturing Company, I have disclosed and claimed more articularly the use of a high voltage and hlgh frequency electric field employed in combination with a member of dielectric material to therebyheat the same. The subject-matter of the present application relates more particularly to the use of a high frequency electromagnetic field when combined with a high frequency electric field in order that material'having a negative temperature coeflicientof resistivity may be initiall heated by subjecting it to the action o the electric field and then further causing its temperature to rise by'subjecting it to the action of an electromagnetic field of high frequency.

' A container 11 for a mass 12 of material to be heated may consist of any suitable or desired material that is an imperfect dielec tric, such as glass or quartz. It is, however, not necessary that the container consist of such material when the mass of material to sufliciently high temperature to be operatedupon consists of material, that has a relatively high inherent resistivit when cold and that has a relatively hig conductivity when hot.

The oxides of metals are examples of such material and they may be operated upon by the means and the system embodying my invention, to cause the same to be heated to ermit of their commercial application, suc 1, for instance, as coatings or other material.

A coil 13 of a suitable electric-conducting material, such as copper, surrounds the con-' tainer 11 and has the terminals thereof connected to the terminals of a suitable source of supply of high frequency electric current, here illustrated as a transformer 14, the secondary winding of which is connected to the coil 13 and the primary winding of which is connected to the terminals of a suitable source of supply. Any suitable source of supply of high frequency alternating or oscillating current is intended to be represented by the transformer 14 and as such sources of supply are well known in the art, I do not consider it necessary to illustrate or describe them in detail. A condenser 15 may be provided, and is preferably of such capacitance as to make the secondary circuit of the transformer resonant at the frequency of the source of current.

A pair of electrodes 16 and 17 are located in spaced relation and are operativcly associated with the container 11. A transformer 18, comprising primary and second ary windings, is illustrated in the drawings as representing a suitable source of high frequency and high voltage current, the terminals of the secondary winding of the transformer being connected to the respective electrodes 16 and 17.

In practicing my method of heating by consecutive or simultaneous subjection of the container and of the mass of material to be heated to the action of high frequency electric and electromagnetic fields,=the source of supply 18 is first energized in order that pyroelectric material 12 within the container 11 may be subjected to the action of the high frequency electric field,.thereby causing heat to be generated in the mass itself and resulting in a rise in temperature thereof.

When this temperature rise is sufficient to effect a substantial decrease in the inherent resistivity of .the material, the source of supply 14 may be energized, thereby causing a high frequency electromagnetic field to be generated by-and within the coil 13.

This electromagnetic field causes a relatively large amount of energy loss in the non-conducting mass of materialand results in a much quicker rise of the temperature therein. As the inherent resistivity of the material decreases with an increase in temperature, it is apparent that it will require a short time only to cause the temperature thereof to be raised to a predetermined value.

When it is desired to heat a mass of material that is conducting even when cold, it is desirable to employ a crucible or container of imperfect dielectric material. Heat is generated in the container 11 by subjecting it to the action of a high frequency electric field generated between the electrodes 16 and 17. The heat generated in the container 11 is imparted to the mass of material to be heated and, depending upon the characteristics of the mass of material, the electromagnetic field may be energized simultaneously with the electric field or after the temperature of the material has beenrai'sed a predetermined amount.

In Fig. 3, l have illustrated a preferred form of device embodying my invention in which a single source of high voltage and high frequency electric current is connected to means for producing respectively an electric field and an electromagnetic field.

A transformer 14 has the terminals of secondary winding electrically connected to the terminals of a coil 13 to thereby produce a high frequency electromagnetic field. Two spaced electrodes 19 and 21, located within the coil 13 are electrically connected to the terminals of the secondary winding of the transformer 14 and a container 22 is located therebetween. The container 22 is preferably of shallow form, and of short length relatively to the axial length of the coil 13, to obtain the proper electric conditions when in operation. It is desirable and may become necessary to slot the electrodes 19 and 21 radially thereof to pre vent excessive temperature rise by reason of eddy current losses therein.

The device and system illustrated in Fig. 3 will operate automatically when employed to heat materials having a negative temperature coefficient of resistivity, in that the material will be, initially heated by the action of the electric field and will then be further heated mainly by the action of the electromagnetic field. Both fields are effective during the entire operation but their action is selective as stated-above.

In case structures, comprising a part of dielectric material, that'may. be influenced tures may, for instance, comprise vacuumtubes, and where large numbers of such tubes are to be operated upon, the furnace structure may be so designed that the de sired heating effects may be obtained in each part of the tube.

I consider that the system embodying my invention will find a distinct field of usefulness in connection with the manufacture of small evacuated bulbs, such as are now used in radio communication work. It is evident that if a conducting material constitutes a part of such a bulb or vacuum tube, it may be-directly acted upon by the electromagnetic field, and that the glass of such a bulb will be heated by energy loss generated) therein when subjected to the action of the high frequency electric field. This makes it possible to effect selective heating of predetermined portions or parts of such apparatus or of similar apparatus and also makes it possible to heat portions thereof to a predetermined temperature by means of the high frequency electric field and to further increase the temperature of a predetermined part of the device by subjecting it to the action of the high frequency electromagnetic field.

Where I have referred to a source of sustained electric current of high frequency, 1 include frequencies not less than those usually employed in radio telegraphy and radio telephony and such higher frequencies as may be commercially produced for such applications. A sustained alternating current of high frequency is particularly applicable for my purpose, as the discharge from a series of high frequency wave trains, such as produced by an oscillatory spark discharge, will not, in many cases, produce the desired heating effects.

Various modifications and changes may be made herein without departing from the spirit and scope of the invention. I desire therefore, that only such limitations shall be placed thereon as are imposed by the prior art.

a I claim as my invention:

1. In a heating system, the combination with a mass of material to be heated and a means for producing a high frequency electromagnetic field, of means for producing a high frequency electric field surrounding said mass.

2. In a heating system, in combination, a mass to be heated,-said mass being pyromagnetic, means for producing, a high frequency electromagnetic field in said mass, and means for producing a high frequency electric field in said mass.

3. In a heating system, in combination, a mass of material to be heated, a coil, a source of high frequency current connected to said coil, and means for subjecting said mass of material to a high'frequency electric field.

4. In a heating system, in combination, a mass of material to be heated, a container therefor, means for producing a high frequency electromagnetic field surrounding said mass of material, and means for producing a high frequency electric field surrounding said mass of material.

5. In a heating system, in combination, a mass of material to beheated, a container therefor, a coil surrounding saidcontaincr, a source of high frequency current electrically connected to saidcoil, a pair of spaced electrodes operatively associated with said container, and means for producing a high frequency electric field between said electrodes.

6. The method of heating a mass of material having a relatively high negative temperature cocfiicient of resistivity that comprises subjecting the mass of material to the action of a high frequency electric field to raise the temperature thereof, and then subjecting it to the action of a high frequency electromagnetic field until the desired temperature is reached.

In testimony whereof, I have hereunto subscribed my name this 17th day of December 1923.

CHESTER 'r. ALLCUTT. 

